Generally, the structure of a motor has mechanical connections of brush and commutator so that when a motor is initially started, a peak current will be always introduced into the motor. This phenomenon results from an improper layout of electric wires and a poor performance of power source. In the past, there is no buffer circuit to prevent the occurrence of peak current. Because the motor is suddenly started from the stationary state, the peak current will bring about a big mechanical shock in the motor thereby resulting in the damage of the motor.
Recently, some methods for eliminating this phenomenon are proposed. One of these methods is to use a protective circuit, such as a capacitor or a variable resistor, disposed near the power source of the motor to protect the motor after a peak current is introduced, but this protective circuit will also be damaged after being used for a long lime. Another method is to stagedly start the motor through a complicated and expensive circuit, for example, using a circuit including a plurality of filters to start the motor by generating a pulse width modulation (PWM) signal to be output to the transistor, wherein the switched interval of the transistor is changed along with a variation of the duty cycle of the PWM signal thereby changing the average current flowing through the motor to further control the rotation speed of the motor. However, such a way of stagedly starting the motor needs a complicated and expensive PWM circuit. In addition, this PWM circuit will introduce an electroacoustic sound while the motor is started and the reliability of internal electronic parts will also be affected under multiple impulsions.
Therefore, it is desirable to develop a simplified and economical starting device and method for improving the above-described defects of the prior art.